The contribution of primary production to the overall organic matter pool in Volga reservoirs

The results of studies of the concentrations and the ratios between the forms of organic matter in Volga reservoirs are presented. The reservoirs under consideration have different morphometric characteristics. flowage, and trophic status. Total organic matter content varies from 7.1 to 11.8 g/m3 or from 39.1 to 70.8 g/m2 with the proportion of labile fraction of 4.4–15.2%. The primary production of plankton, the daily value of which accounts for 14–40% of labile organic matter, has a notable effect on its concentration and input. Organic matter pool in Volga reservoirs forms under the effect of the morphometric features of reservoirs, water exchange, and the drainage area. The total characteristics of organic matter in the Upper Volga reservoirs have not experienced significant changes over the 20-year period. However, data for 2005 show that the contribution of primary production to the total concentration of organic matter and its labile fraction have decreased due to a decline in the productivity of planktonic communities recorded in recent years.